The present invention relates to plasma treatment technology for making a source gas into a plasma and carrying out treatments such as etching, ashing, film deposition, and sputtering etc. on a surface of a solid material such as a semiconductor with physical or chemical mutual reaction of activated particles. In particular, the present invention relates to a plasma treatment apparatus effective for etching a gate or metal during the course of manufacturing a semiconductor device (semiconductor integrated circuit device).
Conventionally, with regard to a plasma treatment apparatus, for the purpose of improving uniformity or stability of plasma for treatment on the surface of a semiconductor material, the following constructions are known.
(a) A plasma treatment apparatus which comprises a dielectric window for introduction of electromagnetic waves into a chamber evacuated to low pressure, and for which size and shape of an opening of dielectric window to the side of the chamber evacuated to low pressure, that is, size and shape of the chamber evacuated to low pressure immediately below the dielectric window is stipulated.
For example, JP-A-11-111696 specification discloses the relationship between size and shape of an opening of a rectangular dielectric window to the side of the chamber evacuated to low pressure and frequency of electromagnetic waves. In addition, JP-A-10-199699 specification discloses the relationship between size and shape of an opening of a circular dielectric window to the side of the chamber evacuated to low pressure and frequency of electromagnetic wave.
(b) A plasma treatment apparatus which comprises a dielectric window for introduction of electromagnetic wave into inside a chamber evacuated to low pressure and an antenna of a disk type, a ring type, and a slot type etc. toward the atmosphere side of the dielectric window, and for which size and shape of the antenna is stipulated.
For example, JP-A-2000-164392 specification discloses the relationship between size and shape of an antenna of a ring type comprised in the atmosphere side of the dielectric window and frequency of electro-magnetic wave. In addition, JP-A-2000-223298 specification discloses the relationship between size and shape of an antenna of a slot type comprised in the atmosphere side of the dielectric window and frequency of electromagnetic wave.
In addition, JP-A-2000-77384 specification, for example, discloses a plasma treatment apparatus related to both of the above described (a) and (b), and control of uniformity of plasma by way of ratio of size and shape of an antenna of a circular type comprised in the atmosphere side of the dielectric window to size and shape of an opening of a circular dielectric window to the side of the chamber evacuated to low pressure.
(c) A plasma treatment method which comprises inside a chamber evacuated to low pressure an antenna for introduction of electromagnetic wave into inside the chamber evacuated to low pressure, and for which size and shape of the antenna is stipulated. For example, JP-A-2000-268994 specification discloses the relationship between size and shape of an antenna comprised inside a chamber evacuated to low pressure and frequency of electromagnetic wave. In addition, JP-A-10-134995 specification discloses the relationship between size and shape of an antenna comprised inside a chamber evacuated to low pressure, which includes the case where walls of a chamber evacuated to low pressure are regarded as a part of an antenna and frequency of electromagnetic wave.
(d) A plasma treatment apparatus for which size and shape of a periphery part of a dielectric window for introduction of electromagnetic wave into inside a chamber evacuated to low pressure or structure and material quality thereof is stipulated.
For example, JP-A-3-68771 specification discloses a plasma treatment apparatus in which a microwave absorber is caused to be equipped in the final end of a microwave transmission line.
Moreover, JP-A-11-354502 specification, for example, discloses a plasma treatment apparatus related to both of the above described (c) and (d), and relationship between the end of the antenna and shape/size of a grounding part with respect to function of the periphery part of the antenna comprised inside the chamber evacuated to low pressure. In addition, JP-A-2000-357683 specification discloses relationship between the end of the antenna and shape/size of a electromagnetic wave corrector made of metal or dielectric with respect to function of the periphery part of the antenna comprised inside the chamber evacuated to low pressure.
In recent years, improvement in uniform treatment performance inside semiconductor wafers with large diameter (300 mmxcfx86 or more) is demanded in plasma treatment utilized for manufacturing semiconductor integrated circuit apparatus, so-called LSI (Large Scale Integrated Circuit). In addition, a wide range of application to the following processing steps in an LSI manufacturing process are demanded.
(1) An application to an etching step that can go with micronization with high anisotropy and selectivity, targeting processing of a gate electrode, a metal film or an insulating film.
(2) An application to an anti-reflective film processing step such as BARC (Bottom Anti-Reflective Coating) etc. prior to the above described etching step and a processing step of a hard mask made of film oxide or film nitride etc.
(3) An application to a trimming step for controlling size of a mask prior to the above described etching step.
(4) An application to a step of processing a trench for device split or a gate side wall spacer that is regarded to require a wide range of controllability on such as angle or shape or roundness, etc.
(5) An application to film deposition step that is regarded to require a wide range of condition setting such as pressure range etc.
(6) An application to a step (post-treatment step) to remove resist and etching remains (etching residue) as well as damage layer after etching treatment.
(7) An application to sputtering.
In particular, just the etching step (etching step including primary gate processing as well as before and after that processing) related to forming of a gate of an MOS transistor may include a lot of steps covering the above described trench processing, anti-reflective film processing, mask processing, processing of making a trimmed mask accompanied hereby, processing of the gate itself, and spacer processing thereafter and an apparatus that has all-round ability enabling to carry out all of them is being demanded.
In addition, due to recent demand for small-amount multi-species production, and also from necessity of application to an LSI such as a system LSI in which a plurality of device structures are mounted in a mixed fashion on the same wafer, extremely highly uniform plasma generation is regarded necessary for processing a wafer with large diameter within a wide condition ranges of 0.1 Pa to 10 Pa in terms of processing pressure, 0.3 to 3 mA/cm2 in terms of ion incident current flux to a wafer with respect to various gas seeds.
The present inventors identified the problems with the existing plasma treatment apparatus in the course of developing the present invention. Those problems will be described below with reference to FIG. 17 and FIG. 18, although those figures pertain to an apparatus considered by the inventors in the course of developing the present invention.
FIG. 17 is a schematic view of a plasma treatment apparatus that the inventors considered. This plasma treatment apparatus comprises a chamber evacuated to low pressure (chamber) 206 shaped as a cylinder on which an object for processing, such as a wafer 200, is disposed. FIG. 17 shows a right half sectional view in the radius direction from the center to the outer periphery of this chamber 206.
According to this plasma treatment apparatus, a dielectric window consisting of a quartz plate 202 and a quartz shower plate 203 is provided in a position facing a wafer stage 201 inside the chamber evacuated to low pressure 206. In addition, the quartz plate 202 and the quartz shower plate 203 are fixed to the chamber evacuated to low pressure 206 with a vacuum seal material 204. In order to generate plasma 205, a gas is introduced into inside the chamber evacuated to low pressure 206, and as for frequency of a high-frequency power source to generate electromagnetic waves for making this gas into plasma, 450 MHz was used. The radius of the quartz glass is designed larger than the radius of the internal wall surface of the chamber evacuated to low pressure 206 by around 23 mm. Here, 23 mm is a size falling outside a range of characteristic length of d=l/4+l/2xc3x97(nxe2x88x921)xc2x1l/8: (n: a positive integer, l=c(light velocity)/f/{square root over (xcex5)}), xcex5:dielectric constant. A gap 207 with a thin air layer is provided on the rear face of the quartz plate 202. An antenna 208 and an antenna spacer 209 made of alumina (Al2O3) are provided near the upper part of the quartz plate 202.
An electric field distribution inside the chamber 206 is shown in FIG. 18. This electric field distribution has been obtained by calculation.
(a) For a plasma density being not more than 2.8xc3x971010 cmxe2x88x923 (equivalent to 1.0 mA/cm2 in terms of incident ion current flux (ICF)), a portion with an intense electric field appears in a region slightly being biased to the center part of the space located above the wafer stage. The plasma is initially generated in this intense electric field portion, and that plasma spreads outward due to diffusion so that a uniform ion current is incident onto a wafer. However, as the plasma density is made to increase to (b) 4.0xc3x9710 cmxe2x88x923 (equivalent to 1.4 mA/cm2 in terms of ICF), or (c) 8.0xc3x971010 cmxe2x88x923 (equivalent to 2.8 mA/cm2 in terms of ICF), as shown by a circle 210, a portion with the intense electric field appears gradually in the periphery part of the chamber evacuated to low pressure, and as shown by a circle 211, will get larger. This made the density increase in the periphery part (in the vicinity of the internal walls of the chamber) inside the chamber evacuated to low pressure 206, and spoiled uniformity.
The present invention has been completed based on recognition of the above described problems by the inventors.
An objective of the present invention is to introduce gases and electromagnetic waves into a chamber evacuated to low pressure to form plasma and alleviate change in a standing wave distribution in a plasma treatment apparatus for treatment of the object for processing.
Another objective of the present invention is to provide a plasma treatment apparatus that can give a stable and continuous plasma generation characteristic while maintaining uniformity of large diameter with a wide range of gas seeds, density and pressure.
Another objective of the present invention is to provide a method of manufacturing a semiconductor device that can be planned to improve throughput.
Among the various aspects of the invention disclosed in the present application, a summary of representative ones will now be given.
The plasma treatment apparatus of the present invention may comprise a chamber feasible to be evacuated to low pressure (chamber), a wafer stage for an object for processing located inside the above described chamber to be disposed thereon, an antenna as well as a dielectric window provided at a location facing the above described object for processing, a high-frequency power source with frequency=f to generate electromagnetic waves for making a predetermined gas to be introduced into the above described chamber into plasma, and a part for controlling a standing wave for making the standing wave electric field distribution provided in the vicinity of the periphery part of the above described dielectric window proper.
The basic construction of the part for controlling the standing wave is a ring structure with the portions other than the entrance thereof being surrounded by conductor and with a mode of a cavity having the final end being sealed with conductor, and inside the cavity is filled with any one of vacuum, air, or a dielectric with dielectric constant xcex5.
In addition, with the radial depth of the chamber (the distance from the entrance to the internal end part of the conductor) d being set equivalent to l/4+l/2xc3x97(nxe2x88x921): (n: positive integer, l=c(light velocity)/f/{square root over (xcex5)}) in terms of characteristic length of the electromagnetic wave or in the vicinity thereof, the standing wave electric field distribution formed inside the dielectric window is made to reach a maximum (that is, a maximum amplitude position of the standing wave) in terms of radial position of an entrance of the standing wave controlling part. Incidentally, the radial position of an entrance of the standing wave controlling part refers to a position of the periphery end part of the dielectric window where the standing wave controlling part is mounted and a position equivalent to the internal wall surfaces of the chamber.
If quality constants of plasma for high frequency, which are described in technical literature on high-frequency plasma, for example, M. A. Lieberman and A. J. Lichtenberg: Principles of Plasma Discharges and Materials Processing, (John Wiley and Sons, Inc.) pp.93-96, pp. 108-110), are expressed by a dielectric constant, they will be expressed by a real number part giving a negative value and an imaginary number part expressing loss in the plasma. A negative dielectric constant means an inductive medium. According hereto, for example, with quality constants of plasma in, for example, a plasma of chloride of 0.4 Pa under plasma density being 2.8xc3x971010 cmxe2x88x923 (equivalent to 1.0 mA/cm2 in terms of an incident ion current flux (ICF: Ion Current Flux)), 4.0xc3x971010 cmxe2x88x923 (equivalent to 1.4 mA/cm2 in terms of ICF), and 8.0xc3x971010 cmxe2x88x923 (equivalent to 2.8 mA/cm2 in terms of ICF), the dielectric constant of the plasma medium can be expressed as xcex5(2.8xc3x971010 cmxe2x88x923)=xe2x88x9210.1+j0.0816, xcex5(4.0xc3x971010 cmxe2x88x923)=xe2x88x9214.9+j0.117, and xcex5(8.0xc3x971010 cmxe2x88x923)=xe2x88x9230.8+j0.233. With these, propagation of electromagnetic waves in a plasma can be analyzed. When an electromagnetic wave comes from a dielectric window into a plasma expressed by the above described quality constants, a change in medium serves to invert relationship between a maximum amplitude position of and a minimum amplitude position of the standing wave electric field distribution in a location equivalent to wall surfaces inside a chamber. Accordingly, distribution of the standing wave electric field formed in the plasma just below the dielectric window material will reach a minimum (that is, a minimum amplitude position of the standing wave) in a location equivalent to wall surfaces inside a chamber. If an entrance of the standing wave controlling part is narrow to a certain extent, plasma will not extend its influence. Therefore, the wavelength of standing wave electric field to be formed inside the standing wave controlling part will hardly be influenced by kinds of gases to be made into plasma and changes in density and pressure.
Accordingly, even if the quality constants of the plasma medium change, for a chamber comprising a standing wave controlling part regulated to have the above described depth, in the radial position that is the same as the inner diameter of the above described chamber evacuated to low pressure, the standing wave electric field distribution formed in the side of the plasma just below the above described dielectric window material will always be a minimum (that is, a minimum amplitude position of the standing wave). This can regulate the electric field in the vicinity of wall surfaces in the side of plasma just below the above described dielectric window material, and the power of the electromagnetic waves is introduced into an effective space region having a constant span with an expected destination above the wafer stage where an object for processing is always disposed.
That is, according to the present invention, the depth of the part for controlling the standing wave will become effective in the case of falling within the range of d=l/4+l/2xc3x97(nxe2x88x921)xc2x1l/8 (n=positive integer l=c(light velocity)/f/{square root over (xcex5)}). Accordingly, under a wide range of conditions, a plasma treatment apparatus that has high uniformity as well as linearity of plasma density for electromagnetic wave invested power and stable and continuous characteristic can be provided.
The part for controlling a standing wave of the present invention is filled with vacuum, air, or a dielectric almost lacking loss inside itself, and is to make the electric field in the vicinity of the internal walls of the chamber proper in terms of size and shape, and therefore will not give rise to bad influences such as loss of power and excess heating in that portion.
In addition, since provision outside the vacuum in the periphery part of the dielectric window is easily feasible, there is no necessity that a ring made of metal material be inserted inside the chamber evacuated to low pressure.
Moreover, the wavelength of the standing wave electric field formed inside the part for controlling the standing wave is approximately constant irrespective of conditions of plasma, and there is no need to change the structure mode from time to time during wafer processing with some moving mechanism.